Re: [PATCH v1 1/1] of: unittest: unflatten device tree on UML when testing
From: Frank Rowand
Date: Thu Feb 14 2019 - 21:48:40 EST
On 2/14/19 5:26 PM, Brendan Higgins wrote:
> On Thu, Feb 14, 2019 at 4:10 PM Frank Rowand <frowand.list@xxxxxxxxx> wrote:
>> On 2/12/19 10:53 AM, Brendan Higgins wrote:
>>> UML supports enabling OF, and is useful for running the device tree
>>> tests, so add support for unflattening device tree blobs so we can
>>> actually use it.
>>> Signed-off-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
>>> drivers/of/unittest.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
>>> index 84427384654d5..effa4e2b9d992 100644
>>> --- a/drivers/of/unittest.c
>>> +++ b/drivers/of/unittest.c
>>> @@ -2527,6 +2527,9 @@ static int __init of_unittest(void)
>>> + if (IS_ENABLED(CONFIG_UML))
>>> + unflatten_device_tree();
>>> pr_info("start of unittest - you will see error messages\n");
>> (Insert my usual disclaimer that I am clueless about UML, I still need to learn
>> about it...)
>> This does not look correct to me.
>> A few lines earlier in of_unittest(), the live devicetree needs to exist for
>> unittest_data_data() and a few of_*() functions to succeed. So it seems
>> that the unflatten_device_tree() for uml should be at the beginning of
> It is true that other functions ahead of it depend on the presence of
> a device tree, but an unflattened tree does get linked in somewhere
> else. Despite that, this is needed for overlay_base_root. I got
> similar behavior if you don't link in a flattened device tree on x86.
> Thus, the order in which you call them doesn't actually seem to
> matter. I found no difference from changing the order in UML myself.
> Without my patch we get the following error,
> ### dt-test ### FAIL of_unittest_overlay_high_level():2372
> overlay_base_root not initialized
> ### dt-test ### end of unittest - 219 passed, 1 failed
> With my patch we get:
> ### dt-test ### end of unittest - 224 passed, 0 failed
Thanks for reporting both the failure and the success cases,
that helps me understand a little bit better.
If instead of the above patch, if you add the following (untested,
not even compile tested) to the beginning of of_unittest():
does that also result in a good test result of:
### dt-test ### end of unittest - 224 passed, 0 failed
I think I need to find some time to build and boot a UML kernel soon.
My current _guess_ is that the original problem was not a failure to
unflatten any present devicetree in UML but instead that the UML
kernel does not call unflatten_device_tree() and thus fails to
indirectly call unittest_unflatten_overlay_base(), which is
called by unflatten_device_tree().
unittest_unflatten_overlay_base() is an unfortunate wart that I
added, but I don't have a better alternative yet.
> I used the following .config for these results:
>> Rob, if I am correct please revert this patch.